Various types and configurations of prosthetic heart valves, used to replace diseased natural human heart valves, are known in the art. The actual shape and configuration of any particular prosthetic heart valve is, of course, dependent to some extent upon the valve being replaced (i.e., mitral valve, tricuspid valve, aortic valve, and pulmonary valve). In general terms, however, the prosthetic heart valve design attempts to replicate the function of the valve being replaced and thus will include valve leaflet like structures. With this in mind, prosthetic heart valves including valve leaflets are generally categorized as either forming relatively flexible leaflets or relatively rigid leaflets.
The category including prosthetic heart valves which form relatively flexible leaflets includes bioprosthetic heart valves having leaflets made of a biological material as well as prosthetic heart valves having leaflets made of synthetic (e.g., polymeric) material. Flexible leaflet prosthetic heart valves are generally categorized as having a frame or stent or as having no stent. The stent in a stented prosthetic heart valve normally includes a substantially circular base or stent ring around which an annular suture material is disposed for suturing the prosthesis to heart tissue. The stent ring including the annular suture material is typically referred to as a sewing ring. Further, the stent forms at least two, typically three, support structures extending from a stent ring. The support structures are commonly referred to as stent posts or commissure posts and can include an internal, rigid yet flexible structure extending from the stent ring, covered by a cloth-like material similar to that of the annular suture material. The stent or commissure posts define the junction between adjacent tissue or synthetic leaflets otherwise secured thereto.
Examples of prosthetic heart valves are described in U.S. Pat. No. 4,106,129 to Carpentier et al. and U.S. Pat. No. 5,037,434 to Lane. These disclosures detail a conventional configuration of three leaflets where one leaflet is disposed between each pair of stent or commissure posts. The Hancock™ II Bioprosthesis, manufactured by Medtronic, Inc., Minneapolis, Minn., is a commercially available example of a bioprosthetic valve. The Hancock™ II is available in various sizes such that it may be implanted in patients having corresponding varying sizes of heart valve annuli.
During valve replacement surgery, the heart valve prosthesis is implanted within the patient's heart using either a supra-annular or intra-annular implant technique. The supra-annular implant technique sutures the prosthetic heart valve above the annulus corresponding to the heart valve to be replaced. The intra-annular implant technique sutures the prosthetic heart valve within the annulus corresponding to the heart valve to be replaced.
Ideally, the heart valve annulus is formed of relatively healthy tissue receptive to some shaping by the surgeon in preparation of receiving the heart valve prosthesis; however, due in part to the space and time constraints during valve replacement surgery, the shape of the resulting annulus is often less than perfect for the attachment of a heart valve prosthesis. At times, the annulus and/or the patient's natural leaflets are calcified, requiring complete annular debridement or removal of the hardened tissue. The annular debridement results in a less defined annulus ledge and larger overall orifice into which, or above which, the prosthetic heart valve is to be attached. As such, the size and contour of each annulus varies widely from patient to patient.
Due to the uneven nature of the annuli, a surgeon needs to select a properly sized prosthetic heart valve to match a particular patient's annulus. Typical annulus sizers are simple cylinders made out of rigid plastics, where the cylinder diameter corresponds to a size of a particular prosthetic heart valve. During surgery, a surgeon typically has a number of sizers at his disposal, each sizer having a different size or diameter (i.e., each sizer relating to a different size of prosthetic heart valve). A surgeon inserts the sizer or a series of different sizers into the valve opening to measure the size of the valve opening. Upon determining the size of the valve opening, the surgeon selects a heart valve prosthesis for implantation having a size believed to correspond to the size of the valve opening. Since the properties of the materials from which current sizers are constructed are often rigid and do not match the properties of actual prosthetic heart valves, it can be difficult to select the appropriate size heart valve for the patient when utilizing such sizers.